Theodoxus gurur Sands & Gloeer sp. nov. Figures 12A, B, 13A-G, 14A-F

Type locality.

Suyunbaşı spring complex, Ayrancılar, İzmir, Turkey; 38.24826°N, 27.28117°E (Figs 3A, 12A, B).

Holotype.

RMNH. MOL.342197 ( Suyunbaşı spring complex, Ayrancılar, İzmir, Turkey; 38.24826°N, 27.28117°E) stored in NMNL: Shell height 5.8 mm, width 6.0 mm (Fig. 13A-D) .

Paratypes.

Twenty four specimens from Suyunbaşı spring complex, Ayrancılar, İzmir, Turkey; 38.24826°N, 27.28117°E: 11 in NMNL (RMNH. MOL.342198, RMNH. MOL.342199; Fig. 13E-G) and 13 in UGSB (UGSB 20689, UGSB 20745, UGSB 20746; Fig. 14A-F) .

Etymology.

The word " gurur " means “pride” in Turkish, referring to the PRIDE (Drivers of Pontocaspian Biodiversity Rise and Demise) programme (also see Acknowledgements). One of its aspects is understanding the evolution of mollusc species in the Pontocaspian and associated satellite regions in Anatolia and the Balkans.

Description.

Shell (Fig. 13A-C, E-G): Hemispherical, transversely slightly elongate, consisting of typically 3-3.5 whorls that rapidly grow. Spire of low to moderate height for Theodoxus; apex often corroded. Shell height ranges from 5-6.5 mm, width from 5.3-7.0 mm. Periostracum uniformly black; surface can be glossy, always finely striated with growth lines. Aperture semicircular; no serrations on the inner lip. Columellar plate smooth, flat to slightly concave, inclined towards aperture; blue-grey in colour.

Operculum (Fig. 13D): Operculum plate made of two parts, calcareous base and conchioline lamella; calcareous base mostly light to dark brown; lamella light yellow-orange. Left adductor of operculum base slightly triangulate, no obvious callus on top right edge. Apophysis distinctively white; broader at top, narrower and attenuated at bottom. Rib-shield strong. Small, short rib-pouch. Small white pseudo-apophysis extends from base of apophysis.

Radula (Fig. 14A-F): R-central tooth flanked by the A-central, B-central, C-central, E-lateral on each side. Additionally, two interconnected layers of marginal teeth occur, encasing central and lateral teeth. R-central with nearly rectangular face, slightly concave anterior edge. A-central large and flat with thin ridge; some curling of ridge on upper edge of cusp. B-central diminished, forms irregular “S” shape. C-central equally diminished, partly hidden below lower edge of E-lateral. E-lateral simple, with no serration on upper edge. First layer of marginal teeth comprises 35-37 teeth, which decrease in size away from E-lateral but increase in size and show serrations on edges of small faces; semidetached from second layer, which is fused and forms outer wall.

Differentiating features.

Using only conchological features of periostracum colouration and patterning and shell shape, the hemispherical, glossy black, and finely striated shells of T. gurur sp. nov. are easily differentiable from T. altenai, which displays light ivory spots on a dark brown-black background (Figs 4A-G, 13A-G), and T. gloeri, which lacks shell pigmentation and bears strong axial ribs on the shell (Figs 11A-C, 13A-G). However, it is still challenging to differentiate T. gurur sp. nov. from some morphotypes of T. anatolicus, T. baeticus, T. fluviatilis, T. jordani, T. macri (G.B. Sowerby II, 1849), T. major Issel, 1865, T. pallidus (Dunker, 1861), T. syriacus (Bourguignat, 1852), T. velox, T. wesselinghi sp. nov., and T. wilkei sp. nov., which can share hemispherical, glossy black, and finely striated shells (Figs 5A-M, 6A-G, 8A-D, 10E-H, 13A-G, 15P-R, 16C-E, O, P, 18A-D, 19O, P, 20A-D, 21I-R, 22I, J, 24H-J, 27A-D). Theodoxus gurur sp. nov. can be distinguished from Anatolian morphotypes of T. baeticus, which typically displays ivory blotches on brown background (Fig. 7A-D); T. jordani, which typically displays brown diagonal zig-zag line patterning on an ivory background (Fig. 15E-L) and T. velox, which tends to have white-ivory stripes on a dark background (Fig. 22K-M). Moreover, T. jordani typically has a lighter columellar plate in comparison (Figs 13, 15 - 17). Finally, the light to dark brown calcareous base of the operculum in T. gurur sp. nov. can help to distinguish it from T. altenai, T. anatolicus, T. baeticus, T. jordani, T. macri, T. major, T. pallidus, T. syriacus, and T. wesselinghi sp. nov., which typically have lighter calcareous bases ranging from ivory to cream or light brown (Figs 4 - 8, 13, 15 - 21, 24); Theodoxus wilkei sp. nov., differs in its bright orange operculum (Figs 13, 27).

More differentiating features occur in the structure of the operculum. These include the attenuated apophysis in T. gurur sp. nov. (Fig. 13), which is lacking or reduced in T. altenai and T. jordani (Figs 4, 15, 17). The lack of or an extremely diminished rib-pouch and rib-shield in T. altenai, T. anatolicus, T. jordani, and T. macri separate these species from T. gurur sp. nov. (Figs 4, 5, 13 15, 17, 18). Additionally, the presence of a pseudo-apophysis differentiates T. gurur sp. nov. from T. fluviatilis, T. major, T. pallidus, T. syriacus, T. velox, T. wesselinghi sp. nov., and T. wilkei sp. nov. (Figs 9, 10, 13, 19 - 22, 24, 27). Theodoxus anatolicus, T. baeticus, T. jordani, and T. macri, in turn, appear to have overall larger pseudo-apophyses (Figs 5 - 8, 13, 15, 17, 18). Finally, the presence of a strongly defined callus on the top edge of the right adductor in T. altenai, T. anatolicus, T. baeticus, T. fluviatilis, T. pallidus, T. syriacus, T. wesselinghi sp. nov., and T. wilkei sp. nov. may help in differentiation from T. gurur sp. nov. (Figs 4 - 10, 13, 20, 21, 24, 27). Also, the more angulated left adductor of the operculum base of this species differs from the rounded left adductor seen in T. syriacus, T. wesselinghi sp. nov., and T. wilkei sp. nov. (Figs 13, 27).

Little is known about the radula of many recognised Theodoxus spp. Based on the available data, T. gurur sp. nov. can be distinguished by the rectangular face of the R-central from T. fluviatilis, T. jordani, T. wilkei sp. nov., and T. wesselinghi sp. nov., which have more square, triangulate or globular faces in comparison (see Baker 1923; Zettler 2008; Figs 14B, 25B, 28B). The smooth upper edge of the E-lateral can be used to distinguish T. gurur sp. nov. from T. wilkei sp. nov. and T. major, which generally have large serrations (see Anistratenko et al. 2017; Fig. 14B, C).

Remarks.

Our results, as well as the phylogeny of Sands et al. (2019a), suggest T. gurur sp. nov. belongs to a large clade of Anatolian and Mediterranean species that includes T. altenai, T. anatolicus, T. baeticus, T. jordani, T. macri, T. marteli, and an undescribed species from Spain (Sands et al. 2019a; Fig. 2). The T. gurur sp. nov. lineage likely diverged from these species during the Pliocene (Fig. 2).

Distribution.

Only known from the type locality (Figs 3A, 12A, B).

Ecology.

The Suyunbaşı spring complex is part of a recreational park that has been heavily altered to channel and pool water for recreational activities (personal observation M.E.G.). The spring floor and channels are made up of a number of small to large stones or coarse sand, while macrophytes are largely absent (Fig. 12A, B). Theodoxus gurur sp. nov. can be found attached to stones and concrete banking and co-occurs with Pseudamnicola sp. (personal observation M.E.G.).